What did President Erdogan say?

"We will start the operation to clear the east of the Euphrates from separatist terrorists in a few days," Mr Erdogan said on a televised speech on Wednesday, referring to territory held by the YPG.

He did not specify which areas would be targeted, but it would be the first time Turkish troops have moved east of the river.

"Our target is never US soldiers," he added. There are some 2,000 US troops currently in Syria, many of them stationed in the north.

Turkey considers the YPG an extension of the banned Kurdistan Workers' Party (PKK), which has fought for Kurdish autonomy in south-eastern Turkey for three decades.

Mr Erdogan wants to prevent the Kurds from consolidating their hold on Syrian territory and forming an autonomous region on the border.

What's the context?

US soldiers have been working closely with Kurdish forces who form part of an alliance - the Syrian Democratic Forces (SDF) - in the battle against the Islamic State (IS) group. Turkey has long criticised this US policy.